In a manufacturing process of a semiconductor device, a process such as a film forming process or the like is performed on a substrate such as a semiconductor wafer or the like. As a film forming method, for example, an ALD (Atomic Layer Deposition) method is available. In a film forming apparatus that forms a film using the ALD method, atomic layers are deposited one by one to form a desired film on a substrate, by repeating a cycle of supplying a precursor into a reaction chamber and purging the interior of the reaction chamber while heating a film formation target substrate. In the film forming apparatus, a mounting table on which a substrate is mounted and a gas supply part for supplying a processing gas to the substrate mounted on the mounting table are opposed to each other in a processing container. The processing gas is supplied from the gas supply part in a shower-like manner.
The above-described gas supply part, which is called a gas shower head or the like, includes a processing gas introduction port and gas supply holes formed in the lowermost portion thereof. In addition, the gas shower head includes a diffusion space provided between the introduction port and the gas supply holes and configured to diffuse a gas in the horizontal direction.
In the gas shower head, the diffusion space is divided into three. The diffusion spaces adjacent to each other are separated by partition walls. Gas supply holes are provided for each diffusion space. The gas shower head can control the supply amount of the processing gas to the substrate by individually adjusting the supply amount of the processing gas to be supplied to each diffusion space. Thus, the gas shower head can form a film with a uniform thickness. Furthermore, in the gas shower head, the central diffusion space is formed in a disc shape in a plan view, the outermost diffusion space is formed in an annular shape in a plan view, and the intermediate diffusion space positioned between the central diffusion space and the outermost diffusion space is also formed in an annular shape in a plan view. In addition, in the gas shower head, as shown in FIG. 10A, a plurality of processing gas introduction ports P having a circular shape in a plan view are formed at the positions overlapping, in a plan view, with the diffusion space S having an annular shape in a plan view.
However, when the introduction ports P are formed at the positions overlapping, in a plan view, with the diffusion space S having an annular shape in a plan view, a region R in which the concentration of the processing gas becomes thin is generated in a part of the outer peripheral portion of the diffusion space S. In other words, the concentration of the processing gas in the diffusion space S becomes non-uniform in the circumferential direction. By reducing the thickness of the diffusion space S in the vertical direction, it is possible to reduce the area of the region R as shown in FIG. 10B. However, it is difficult to eliminate the region R. If the region R in which the concentration of the processing gas becomes thin is present in a part of the outer peripheral portion of the diffusion space S as described above, the concentration of the processing gas in the space on the substrate just below the region R becomes thinner than in other portions. Furthermore, if the introduction ports P are formed at the positions overlapping, in a plan view, with the diffusion space S having an annular shape in a plan view, the concentration of the processing gas in the space on the substrate just below the introduction ports P becomes higher than other portions.
Therefore, if the introduction ports P are formed at the positions overlapping, in a plan view, with the diffusion space S having an annular shape in a plan view as in the above-described gas shower head, it is difficult to uniformly form a film having a desired film thickness. Furthermore, when the above-described gas shower head is used in a processing apparatus for etching a substrate, it is difficult to uniformly perform etching with a desired thickness for the same reason as described above.